Transcript pathogenesis

pathogenesis
Fig. 1-15
KOCH’S POSTULATES
The Postulates:
Tools:
1. The suspected pathogenic
organism should be
present in all cases of the
disease and absent from
healthy animals.
Microscopy, staining
2. The suspected organism
should be grown in pure
culture.
Laboratory culture
Diseased
animal
Red
blood
cell
Observe
blood/tissue
under the
microscope
Suspected
pathogen
Streak agar plate
with sample
from either
diseased or
healthy animal
Colonies of
suspected
pathogen
Healthy
animal
Red
blood
cell
No
organisms
present
Inoculate healthy animal with
cells of suspected pathogen
3. Cells from a pure culture
of the suspected organism
should cause disease in a
healthy animal.
Experimental animal
Diseased animal
Remove blood or tissue sample
and observe by microscopy
4. The organism should be
reisolated and shown to be
the same as the original.
Laboratory reisolation
Suspected
pathogen
Laboratory
culture
Pure culture
(must be
same
organism
as before)
• Primary pathogens: Cause disease in healthy hosts
• Opportunisitc pathogens: Cause disease only in
immunocompromised patients
• Virulence is a measure of the severity of a disease.
•
- Infectious dose vs. lethal dose
Figure 25.5
Figure 25.6
Figure 25.11
Figure 25.13A
Table 28-3
Streptococcus pyogenes M protein
Bordetella pertussis Pertactin
Figure 25.14
Bacteria can attach to surfaces
in bulk, forming a biofilm.
- Play important roles in
chronic infections
Figure 25.15A
Figure 25.16
AB Toxins
• B subunit: Binds to host cell
•
- Delivers A subunit to
cytoplasm
•
- Often five B subunits
form a pore for A entry.
A subunit: Has toxic
activity
- ADPribosyltransferase
- Diphtheria toxin
- Cholera toxin Figure 25.17B
Figure 25.17A
Figure 13.7A
Figure 25.20
ADP-Ribosylating Toxins
• Animation: Cholera Toxin Mode of Action
Click box to launch animation
Alpha Toxin
• The hemolytic alpha toxin is produced by
Staphylococcus aureus.
•
- Forms a transmembrane, seven-member pore in
target cell membranes
Figure 25.18
Anthrax Toxin
• Made by Bacillus anthracis
• Two active toxins:
•
- Edema factor raises
cAMP levels.
•
- Causes fluid
secretion, tissue swelling
•
- Lethal factor cleaves
protein kinases.
•
system
- Blocks immune
from attacking
Figure 25.21C
Endotoxins
• Made only by Gram-negative bacteria
• Present in lipopolysaccharide of outer membrane
•
•
- Lipid A released as bacteria die
- Causes massive release of cytokine from host
cells
•
- Can trigger fever, shock, and death
Figure 25.22
Figure 25.31
Figure 25.32
Figure 25.29